The dissolution of a basic pharmacologically active substance increases under the acidic conditions of the alimentary canal, because a basic pharmacologically active substance is usually more soluble under acidic conditions. Therefore, the basic pharmacologically active substance is expected to exhibit the improved absorption in the alimentary canal. However, the absorbency of a basic pharmacologically active substance in the alimentary canal is difficult to improve merely by mixing the basic pharmacologically active substance with an acidic material, because the acidic material elutes, etc., soon after administration. Among basic pharmacologically active substances, particularly poorly soluble basic pharmacologically active substances often fail to achieve expected medicinal actions when taken orally, because they are not satisfactorily absorbed in the alimentary canal.
In order to enhance the absorbency of poorly soluble pharmacologically active substance in the alimentary canal, absorbefacients have often been used. However, absorbefacients have problems in terms of safety, because they may cause mucous membrane disorders, and/or enhance absorbency of components other than the target pharmacologically active substance.
The following methods have been reported for improving the absorbency of pharmacologically active substances. It has been reported that the absorbency of a pharmacologically active substance can be enhanced by combining a higher alcohol, a fatty acid or like oleophilic substance together with a pharmacologically active substance that is poorly soluble when orally taken (see Patent Document 1). It has also been reported that the absorbency of a pharmacologically active substance can be improved by using a hydrophobic pharmacologically active substance in combination with a hydrophilic surfactant and a hydrophobic surfactant (see Patent Document 2). Furthermore, it has also been reported that absorbency of a pharmacologically active substance can be improved by using a hydrophilic pharmacologically active substance together with at least two surfactants (see Patent Document 3). However, merely by using a pharmacologically active substance together with an oleophilic substance or using specific surfactants in combination, satisfactory absorbency of pharmacologically active substance cannot be attained, and therefore it is difficult to satisfactorily absorb a poorly soluble pharmacologically active substance in the alimentary canal.
In light of such problems of the prior art techniques, development of a pharmaceutical composition having excellent basic pharmacologically active substance absorbency, and in particular, a pharmaceutical composition of which poorly soluble basic pharmacologically active component can be satisfactorily absorbed in the alimentary canal so that its medicinal action can be efficiently achieved in vivo, has been awaited.
[Patent Document 1] Japanese Unexamined Patent Publication No. 1998-231254
[Patent Document 2] WO00/50007
[Patent Document 3] WO01/012155